Remove checks & workarounds for unsupported compilers.
Match minimum supported versions from the WIKI [0] by raising them to:
- GCC 9.3.1
- CLANG 8.0
- MVCS 2019 (16.9.16 / 1928)
Details:
- Add CMake checks that ensure supported compiler versions early on.
- Previously GCC per-processor version checks served to exclude __clang__, in some cases this has been replaced by explicitly excluding __clang__. This was needed as CLANG treated some of these flags differently to GCC, causing the build to fail.
- Remove USE_APPLE_OMP_FIX GCC-4.2 OpenMP workaround.
- Remove linking error workaround for old MSVC versions.
[0]: https://wiki.blender.org/wiki/Building_Blender